In general, an electric propulsion aircraft employing a regenerative fuel cell (RFC) system simultaneously uses a solar cell and a fuel cell. For example, for a long flight, a portion of energy obtained by a solar cell is used for flight energy during the daytime, residual energy is stored in a tank in the form of gas of hydrogen and oxygen formed via electrolysis of water and, then, power is acquired using hydrogen and oxygen that are stored in the fuel cell at nighttime when sunlight is not present to maintain propulsion force. That is, an electric propulsion aircraft employing an RFC system charges/discharges electricity via a fuel cell device and a water electrolysis device using a reactant, an oxide, a reduced substance, or the like as fuel.
The electric propulsion aircraft employing the RFC system uses the largest amount of energy during take-off. The electric propulsion aircraft employing the RFC system takes off at a time point when solar energy is highest and also stores hydrogen and oxygen gas in a hydrogen and oxygen tank at maximum pressure to ensure as much energy as possible during take-off. This is because it is possible to obtain maximum output when electrochemical reaction occurs between hydrogen and oxygen that are stored at maximum pressure. That is, power required for take-off may be sufficiently ensured via electrochemical reaction by storing hydrogen and oxygen gas at maximum pressure. In addition, the electric propulsion aircraft employing the RFC system needs to vacate a water tank for storing water generated via hydrogen and oxygen bond and, thus, there is a problem in that sufficient energy for take-off is not stored to degrade a freedom degree of design.
In this regard, Korean Patent Laid-Open Publication No. 10-2004-0008414 (“Operating system for unmanned aerial vehicle” published on Jan. 31, 2004, hereinafter referred to the cited reference) discloses an unmanned aerial vehicle using a solar cell and an internal combustion engine. However, the cited reference has a problem in that sufficient energy is not ensured during take-off.